U.S. patent number 10,044,016 [Application Number 15/214,126] was granted by the patent office on 2018-08-07 for storage battery.
This patent grant is currently assigned to GS Yuasa International Ltd., KYOTO UNIVERSITY. The grantee listed for this patent is GS Yuasa International Ltd., KYOTO UNIVERSITY. Invention is credited to Hajime Arai, Tadashi Kakeya, Akiyoshi Nakata, Zempachi Ogumi, Kenichi Saito.
United States Patent |
10,044,016 |
Kakeya , et al. |
August 7, 2018 |
Storage battery
Abstract
A storage battery includes a negative electrode including, as an
active material, at least one of a metal capable of forming a
dendrite and a metal compound thereof, a positive electrode, a
separator, and an electrolyte containing an additive. In the
storage battery, a concentration of the additive in the electrolyte
in a region on a side of the negative electrode defined by the
separator is higher than a concentration of the additive in a
region on a side of the positive electrode.
Inventors: |
Kakeya; Tadashi (Kyoto,
JP), Saito; Kenichi (Tokyo, JP), Nakata;
Akiyoshi (Kyoto, JP), Arai; Hajime (Kyoto,
JP), Ogumi; Zempachi (Kyoto, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
GS Yuasa International Ltd.
KYOTO UNIVERSITY |
Kyoto-shi, Kyoto
Kyoto |
N/A
N/A |
JP
JP |
|
|
Assignee: |
GS Yuasa International Ltd.
(Kyoto, JP)
KYOTO UNIVERSITY (Kyoto, JP)
|
Family
ID: |
57795732 |
Appl.
No.: |
15/214,126 |
Filed: |
July 19, 2016 |
Prior Publication Data
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|
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Document
Identifier |
Publication Date |
|
US 20170033345 A1 |
Feb 2, 2017 |
|
Foreign Application Priority Data
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Jul 30, 2015 [JP] |
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2015-151179 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M
10/26 (20130101); H01M 10/24 (20130101); H01M
2/164 (20130101); H01M 2/1653 (20130101); H01M
4/24 (20130101); H01M 4/405 (20130101); H01M
4/382 (20130101); H01M 10/30 (20130101); H01M
10/052 (20130101); H01M 10/0567 (20130101); H01M
2300/0014 (20130101); Y02E 60/10 (20130101) |
Current International
Class: |
H01M
2/16 (20060101); H01M 4/24 (20060101); H01M
10/24 (20060101); H01M 10/26 (20060101); H01M
10/052 (20100101); H01M 10/0567 (20100101); H01M
10/30 (20060101); H01M 4/38 (20060101); H01M
4/40 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
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2003297375 |
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2005123059 |
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2009093983 |
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JP |
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2013084349 |
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JP |
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2014044908 |
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Mar 2014 |
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JP |
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2014049352 |
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Mar 2014 |
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JP |
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2014199815 |
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Oct 2014 |
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JP |
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Primary Examiner: Barcena; Carlos
Attorney, Agent or Firm: Rankin, Hill & Clark LLP
Claims
What is claimed is:
1. A storage battery comprising: a negative electrode including, as
an active material, at least one of a metal capable of forming a
dendrite and a metal compound thereof; a positive electrode; a
separator; and an electrolyte containing an additive, wherein the
additive can move in the electrolyte through diffusion or
migration, a concentration of the additive in the electrolyte in a
region on a side of the negative electrode defined by the separator
is higher than a concentration of the additive in a region on a
side of the positive electrode, and the electrolyte is an alkaline
electrolyte solution.
2. The storage battery according to claim 1, wherein the separator
is a semipermeable membrane.
3. The storage battery according to claim 1, wherein the separator
is an ion-exchange membrane.
4. The storage battery according to claim 1, wherein the additive
is a substance capable of enhancing charge-discharge
characteristics of the negative electrode.
5. The storage battery according to claim 1, wherein the additive
is a substance capable of reducing the solubility of at least one
of the metal capable of forming a dendrite and the metal compound
thereof in the electrolyte.
6. The storage battery according to claim 1, wherein the additive
is an organic substance.
7. The storage battery according to claim 1, wherein a viscosity of
the electrolyte in the region on the negative electrode side is 70
Pas or less.
8. The storage battery according to claim 1, wherein the maximum
operating potential of the positive electrode is 0.4 V or more
relative to a potential of an electrode of Hg/HgO.
9. The storage battery according to claim 1, wherein the separator
is an anion-exchange membrane.
10. The storage battery according to claim 1, wherein the separator
is an ion-exchange membrane, and the ion-exchange membrane contains
polyolefin as a substrate.
11. A storage battery comprising: a negative electrode including,
as an active material, at least one of a metal capable of forming a
dendrite and a metal compound thereof; a positive electrode; a
separator; and an electrolyte containing an additive, wherein the
additive can move in the electrolyte through diffusion or
migration, a concentration of the additive in the electrolyte in a
region on a side of the negative electrode defined by the separator
is higher than a concentration of the additive in a region on a
side of the positive electrode, and the separator is a grafted
membrane.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of Japanese patent application
No. 2015-151179 filed on Jul. 30, 2015, which is incorporated by
reference.
FIELD
The present invention relates to a storage battery.
BACKGROUND
In recent years, in association with size reduction and weight
saving of electronic equipment, demands for a high energy density
battery as a power supply are increasingly growing. A storage
battery in which a metal such as lithium, zinc or the like is
contained in the negative active material has an advantage that
energy density per unit mass and power density are high. Such
storage batteries are studied to be used practically as a power
supply of electronic equipment and vehicles.
However, there is a problem that a dendrite may grow from the metal
such as lithium and zinc contained in the negative active material
to cause shortage due to penetration of a separator and the
dendrite causes a charge-discharge cycle life to decrease. Thus, an
additive is conventionally added to an electrolyte against such a
problem.
JP-A-2013-84349 discloses "an electrolyte solution for an alkaline
battery, wherein the electrolyte solution contains at least an
organic substance having two or more carbon atoms and one or more
hydroxyl groups in its molecule." See claim 1.
It is an object of JP-A-2013-84349 "to provide an electrolyte
solution for an alkaline battery and an alkaline battery which
suppress generation of a hydrogen gas produced by a side reaction,
a dendrite formed when zinc is precipitated, and a change in shape
of zinc and can realize a prolonged charge-discharge cycle and an
excellent charge-discharge efficiency." See paragraph [0007].
Further, it is disclosed that "the number of hydroxyl groups is
preferably 5 or less", and a monohydric alcohol, a dihydric alcohol
and a trihydric alcohol which have 2 to 6 carbon atoms are
exemplified as the organic substance. See paragraphs [0017], [0019]
and [0020].
JP-A-2009-93983 discloses "a secondary battery in which a negative
electrode and a positive electrode are arranged with an electrolyte
solution interposed therebetween, wherein the negative electrode
includes, as a negative active material, a material which
absorbs/releases metal ions, and the electrolyte solution includes
at least one dendrite forming inhibitor selected from the group
consisting of polyalkylene imines, polyallylamines and asymmetrical
dialkyl sulfones." See claim 1. Also, it is disclosed that "the
negative electrode includes a material selected from the group
consisting of zinc, magnesium, aluminum and an alloy thereof." See
claim 6.
It is a main object of JP-A-2009-93983 "to provide a secondary
battery capable of performing charge-discharge repeatedly
suppressing formation of a dendrite." See paragraph [0005].
Further, it is disclosed that in a zinc-air battery including, as
an electrolyte solution, a 6N hydroxy aqueous solution containing
polyethyleneimine (PEI) added in an amount of 1 wt %, the formation
of a dendrite is suppressed and charge-discharge could be performed
repeatedly. See paragraph [0018].
JP-A-2003-297375 discloses "an alkaline zinc battery including a
negative electrode containing zinc or a zinc alloy as a negative
active material, a positive electrode, a separator, and an alkaline
electrolyte solution, wherein the alkaline electrolyte solution is
formed by including a cationic organic substance in a 10 wt % to 30
wt % potassium hydroxide aqueous solution." See claim 1. Further,
it is proposed that the cationic organic substance is "any one or
more of a quaternary ammonium salt, a quaternary phosphonium salt,
and a tertiary sulfonium salt," and "the alkaline zinc battery . .
. which is a secondary battery." See claims 2 and 7.
It is an object of JP-A-2003-297375 "to realize an alkaline zinc
secondary battery which prevents expansion and liquid leakage of a
battery associated with generation of a hydrogen gas, and an
internal short-circuit due to nonuniform growth of dendric or
spongy zinc in a zinc negative electrode, and is excellent in
liquid leakage and a cycle life." See paragraph [0076].
Further, in Example of alkaline zinc secondary battery, "n-dodecyl
trimethyl ammonium chloride" and a long chain alkyl trimethyl
ammonium salt are disclosed for the cationic organic substance to
be added to an electrolyte solution. See paragraphs [0171] to
[0245]. Further, it is proposed that "it is preferred that a
concentration of a potassium hydroxide aqueous solution is set to
30 wt % or less in order to surely dissolve the cationic organic
substance in 0.1M or more and a saturated amount or less." See
paragraph [0216]. Also, it is disclosed that "it is found that
liquid leakage and an internal short-circuit of the alkaline zinc
secondary battery are significantly suppressed when the number of
carbon atoms of the long chain alkyl group of the cationic organic
substance is 3 or more," and "however, when the substituent has 15
or more carbon atoms, particularly 21 or more carbon atoms, a
discharge capacity is reduced, and therefore the number of carbon
atoms of the long chain alkyl group of the cationic organic
substance is 3 to 20, and particularly preferably 3 to 15." See
paragraph [0229].
JP-A-2014-199815 discloses "an electrode surface coating forming
agent including a nitrile compound." See paragraph [0001]. As a
problem to be solved, it is shown that "an improvement of stability
of an electrolyte solution at high-temperature is required in order
to improve the safety of a lithium ion battery." See paragraph
[0003]. With respect to the nitrile compound, it is disclosed that
"charge-discharge efficiency can be increased because a stable
protective film is formed on the surface of the electrode by these
compounds," and "further, a dendrite phenomenon of lithium metal
can be suppressed by the stable protective film." See paragraph
[0051]. Also, it is disclosed that "a compound having a nitrile
group used for the electrode surface coating forming agent of the
present invention may be used alone; however, it is contained in an
organic solvent-based electrolyte solution commonly used in an
amount of usually about 0.1 to 80 wt %, preferably about 1 to 50 wt
%, and more preferably about 5 to 30 wt %." See paragraph
[0052].
In JP-A-2014-44908, with respect to "a metal air battery" in which
an electrode active material is "metal zinc" (claims 1, and 11), it
is disclosed that "the air electrode 6 may be disposed so as to be
in contact with an ion-exchange membrane 8 which is in contact with
an electrolyte solution 3 stored in an electrolyte solution tank
1," and "the ion-exchange membrane 8 may be an anion exchange
membrane." Further, it is disclosed that "since the anion exchange
membrane has a cation group serving as a fixed ion, the cation in
the electrolyte solution cannot conduct to the air electrode 6. In
contrast with this, since hydroxide ions produced at the air
electrode 6 are anions, they can conduct to the electrolyte
solution. From this, a battery reaction of a metal air battery 45
can proceed, and the cation in the electrolyte solution 3 can be
prevented from moving to the air electrode 6. From this,
precipitation of metal or a carbonate compound at the air electrode
6 can be suppressed."
JP-A-8-130034 discloses "a Li secondary battery, wherein the
battery has a positive electrode layer on a porous insulating film
side and a negative electrode layer on a cation exchange membrane
side of a separator composed of the electrolyte solution-retainable
porous insulating film and the cation exchange membrane." See claim
1. As a problem to be solved, it is shown that "a problem of a
shortened battery life is significant as lithium or a lithium
alloy, particularly a lithium alloy in which lithium is rich is
used for the negative electrode for the purpose of improving an
electromotive force or a charge-discharge capacity." See paragraph
[0003]. Further, it is disclosed that "addition of a cation
exchange membrane to a negative electrode layer side of a
conventional separator made of a porous insulating film prevents or
inhibits lithium from becoming a compound on the surface of the
negative electrode to be precipitated." See paragraph [0008].
In JP-A-2005-123059, it is disclosed "an air zinc battery in which
an air diffusing layer, a water-repellent film, a positive
electrode catalyst layer, and a separator are layered in turn on a
positive electrode case having air holes, and a gel-like zinc
negative electrode housed in a negative electrode container is
opposed to the positive electrode catalyst layer with the separator
interposed therebetween, wherein the separator has a first layer
made of a semipermeable membrane or a microporous membrane and a
second layer made of a nonwoven fabric or a woven fabric, and the
separator is arranged so that the second layer is positioned on the
positive electrode catalyst layer side." (See claim 1.) Also, it is
proposed that "the nonwoven fabric or the woven fabric arranged on
the positive electrode catalyst layer side of the separator is
excellent in liquid retainability compared with the semipermeable
membrane and the microporous membrane, and water and hydroxide ions
move smoothly by reducing contact resistance between the separator
and the catalyst layer," and "particularly, it is possible to
suppress an increase of internal resistance resulting from lack of
an electrolyte solution in the separator on the catalyst layer
side." See paragraph [0014].
JP-A-60-136182 discloses "an air battery including a gel-like zinc
cathode formed by mixing an amalgamated zinc powder, an alkaline
electrolyte solution and a gelating agent." Also, it is proposed
that "the alkaline electrolyte solution includes sodium hydroxide
or a potassium hydroxide aqueous solution, a concentration of the
solution is 4 to 12 mold, a mixing ratio is set to a range of 0.3
to 3 wt %, the gelating agent includes a carboxyvinyl polymer
having a molecular weight of 100000 to 5000000, and a mixing ratio
of the gelating agent is 0.3 to 3 wt %."
SUMMARY
The following presents a simplified summary of the invention
disclosed herein in order to provide a basic understanding of some
aspects of the invention. This summary is not an extensive overview
of the invention. It is intended to neither identify key or
critical elements of the invention nor delineate the scope of the
invention. Its sole purpose is to present some concepts of the
invention in a simplified form as a prelude to the more detailed
description that is presented later.
In JP-A-2013-84349, JP-A-2009-93983, JP-A-2003-297375 and
JP-A-2014-199815, there are proposed that in storage batteries
including, as a negative active material, a metal such as lithium
or zinc capable of forming a dendrite, the formation of the
dendrite is suppressed by a specific additive for reducing the
solubility of the metal in the electrolyte.
However, since these additives are low in stability at a high
potential, they are decomposed and disappear in a region on a
positive electrode side to deteriorate charge-discharge efficiency,
and therefore practical realization thereof is difficult.
JP-A-2014-44908 discloses that an anion exchange membrane for a
separator is used in a metal air battery to prevent cations from
moving to a positive electrode in an electrolyte to suppress
precipitation of metal at a positive electrode.
JP-A-8-130034 discloses that it can be suppressed that lithium is
precipitated as a compound on the surface of the negative electrode
by arranging a separator made of a cation exchange membrane on a
negative electrode side of a battery in which lithium or a lithium
alloy is used in the negative electrode.
However, JP-A-2014-44908 and JP-A-8-130034 disclose no electrolyte
in which an additive is added for suppressing the formation of
dendrite in a storage battery.
JP-A-2005-123059 discloses a zinc-air battery in which a separator
is arranged so that a first layer made of a semipermeable membrane
or a microporous membrane is positioned on a gel-like zinc
electrode side. Therefore it is said that in the zinc-air battery,
a gelating agent is added to the electrolyte in contact with the
semipermeable membrane on the zinc electrode side. However, as
disclosed in JP-A-60-136182, the gelating agent of the zinc
electrode is the additive having a molecular weight of 100000 to
5000000 to be added to an electrolyte and gelating the electrolyte,
and therefore it is hard to think that the gelating agent moves to
an air electrode side.
It is an object of the present invention to provide a storage
battery having excellent charge-discharge performance by inhibiting
an additive in an electrolyte for suppressing a formation of
dendrite from decomposing/disappearing in a region on a positive
electrode side or from causing a side reaction even when the
storage battery includes a metal capable of forming dendrite in a
negative active material.
A storage battery according to a first aspect of the present
invention includes: a negative electrode including, as an active
material, at least one of a metal capable of forming a dendrite and
a metal compound thereof, a positive electrode; a separator; and an
electrolyte containing an additive, wherein the additive can move
in the electrolyte through diffusion or migration, and a
concentration of the additive in the electrolyte in a region on a
side of the negative electrode defined by the separator is higher
than a concentration of the additive in a region on a side of the
positive electrode.
BRIEF DESCRIPTION OF DRAWINGS
The foregoing and other features of the present invention will
become apparent from the following description and drawings of an
illustrative embodiment of the invention in which:
FIG. 1 shows a conceptual view of liquid separation in a storage
battery according to the present invention.
FIG. 2 shows a schematic view of a two chamber type cell used for a
permeation test.
FIG. 3 is a graph showing a relation between a molecular weight of
an additive and permeability for the additive in the permeation
test.
DESCRIPTION OF EMBODIMENTS
A storage battery according to a first aspect of the present
invention includes: a negative electrode including, as an active
material, at least one of a metal capable of forming a dendrite and
a metal compound thereof (a metal compound of the metal capable of
forming a dendrite); a positive electrode; a separator; and an
electrolyte containing an additive, wherein the additive can move
in the electrolyte through diffusion or migration, and a
concentration of the additive in the electrolyte in a region on a
side of the negative electrode defined by the separator is higher
than a concentration of the additive in a region on a side of the
positive electrode.
The separator may be a semipermeable membrane.
The separator may be an ion-exchange membrane.
The additive may be a substance capable of enhancing
charge-discharge characteristics of the negative electrode in the
storage battery.
The additive may be a substance capable of reducing the solubility
of the metal capable of forming a dendrite and a metal compound
thereof in the electrolyte.
The additive may be an organic substance.
The viscosity of the electrolyte in the region on the negative
electrode side may be 70 Pas or less.
The electrolyte may be an alkaline electrolyte solution.
The maximum operating voltage of the positive electrode may be 0.4
V or more relative to a potential of an electrode of Hg/HgO.
The separator may be an anion-exchange membrane.
The separator may be a grafted membrane.
The ion-exchange membrane may contain polyolefin as a
substrate.
A storage battery according to another aspect of the present
invention includes: a negative electrode including, as an active
material, at least one of a metal capable of forming a dendrite and
a metal compound thereof, a positive electrode; a separator; and an
electrolyte containing an additive, wherein the electrolyte is
liquid, and a concentration of the additive in the electrolyte in a
region on a side of the negative electrode defined by the separator
is higher than a concentration of the additive in a region on a
side of the positive electrode.
It is possible to provide a storage battery having excellent
charge-discharge cycle performance by employing means according to
the present invention.
A storage battery according to the present invention has a negative
electrode including, as an active material, at least one of a metal
capable of forming a dendrite and a metal compound thereof, a
positive electrode, a separator and an electrolyte containing an
additive. The storage battery is configured in such a way that
movement of the additive is suppressed by the separator and a
concentration of the additive in the electrolyte in a region on a
side of the negative electrode defined by the separator is higher
than a concentration of the additive in a region on a side of the
positive electrode. If the concentration of the additive in a
region on the negative electrode side is even slightly higher than
the concentration on the positive electrode side when the storage
battery is left at rest without being charged or discharged, the
effect of the present invention can be exerted. In addition, uneven
distribution of ions or the additive in the electrolyte which is
temporarily generated during charge-discharge of a storage battery
is not included in the present invention because ions or the
additive are uniformly diffused when the storage battery is not
charged or discharged, resulting in decomposition on the positive
electrode side.
In order to realize this battery structure, it is preferred to use,
as a separator to isolate the positive electrode from the negative
electrode, a membrane having such selective permeability that ions
contributing to a battery reaction permeate a membrane but the
permeability for the additive is lower than that for the ions.
Further, it is more preferred to use a membrane (semipermeable
membrane) having selective permeability based on a molecular
weight. In the case of the semipermeable membrane, a flexibility of
battery design can be increased since a molecular weight which can
permeate the membrane can be relatively easily adjusted by
adjusting a pore size or the like.
Further, the separator is more preferably an ion-exchange membrane
because ions contributing to a battery reaction can easily permeate
the ion-exchange membrane.
A conceptual view of the above battery structure is shown in FIG.
1. A separating membrane (separator) of FIG. 1 is preferably a
semipermeable membrane or an ion-exchange membrane in which the
permeability for the additive is lower than the permeability for
the ions contributing to a battery reaction.
Here, the following permeation test was performed on a membrane
formed by graft-polymerizing acrylic acid to a polyethylene film
having a thickness of 25 .mu.m used in experiments of the present
invention (hereinafter, referred to as a "grafted membrane") as a
test for verifying a selective permeability of the membrane to be
used for the separator.
<Permeation Test>
A two chamber type cell as shown in FIG. 2 was prepared, a
separating membrane (separator) made of a grafted membrane of 12 cm
in diameter (diameter of a communicating section of the two chamber
type cell is 12 cm) was disposed between two chambers as a
partition. 10 ml of water was put in one chamber and 10 ml of an
aqueous solution in which each additive shown in Table 1 was
dissolved in an amount of 10% by mass was put in the other
chamber.
The two chamber type cell was stored at 25.degree. C. for 10 days,
and then an amount of carbon contained in water in the chamber in
which the additive was not added was measured. Based on the
measured carbon amount, a permeated amount equivalent to the
content of the additive was determined.
Further, the case in which the additive concentrations in the two
chambers were the same (the permeated amounts equivalent to the
content of the additive were each 5% by mass) was taken as
permeability of 100% to determine permeability of the grafted
membrane for each additive. The results thereof are shown in Table
1 and FIG. 3.
TABLE-US-00001 TABLE 1 Permeated Permeated Amount on the Amount on
the Additive Additive Molecular Equivalent Basis Equivalent Basis
Additive Weight mass % Permeability mass % Permeability
Polyethylene glycol 400 2.3 46% Polyethylene glycol 1000 0.21 4.1%
5.10 102% Polyvinyl alcohol 5800 0.018 0.4% Polyvinyl alcohol 11000
0.023 0.5% Polyvinyl alcohol 22000 0.013 0.3% 0.55 11% Modified
polyvinyl alcohol 44000 0.040 0.8% Modified polyvinyl alcohol 75000
0.072 1.4% Modified vinyl alcohol: modified by substituting a
hydroxyl group with another hydrophilic functional group
As a result of the permeation test, it was found that the
permeability of the membrane decreases as the molecular weight of
the additive increases, and the membrane has selective permeability
based on a molecular weight. In addition, in the present invention,
the case of not having permeability is defined as the case of
exhibiting permeability less than 5% in the above-mentioned
permeation test. That is, it is said that the membrane used in the
present experiment exhibits selective permeability for the additive
having a molecular weight of 1000 or more. Further, the permeation
test of a 4M potassium hydroxide solution was performed by the same
method as the above method, and consequently it was found that
potassium ions and hydroxide ions permeate the membrane.
Accordingly, a storage battery can be obtained which keeps the
concentration of the additive in a region on the negative electrode
side higher than the concentration in a region on the positive
electrode side by arranging, in a region on the negative electrode
side, an electrolyte containing an additive which enhances battery
characteristics, arranging, in a region on the positive electrode
side, an electrolyte containing the additive which is less than
that in a region on the negative electrode side, and using the
membrane as a separator.
As the additive according to the present invention, any of an
inorganic substance and an organic substance may be used as long as
the separator exhibits the selective permeability for the
substance. Among these substances, the organic substance easily
generates gas such as carbon dioxide by decomposition on the
positive electrode, and therefore it easily causes disadvantages
that deformation of a battery occurs in a sealed battery. Thus, it
is preferred that the additive is combined with a separator having
selective permeability since it is easy to ensure a flexibility of
battery design, for example, facilitating sealing of a battery even
when the organic substance additive is used.
The additive may be any additive as long as it has performance for
enhancing charge-discharge characteristics of the storage battery.
The additive is preferably one which enhances charge-discharge
characteristics of the negative electrode, and particularly
preferably a substance capable of reducing the solubility of the
metal capable of forming a dendrite and the metal compound thereof
in the electrolyte by having a function of forming a stable coating
on the negative active material, or like. For example, it is
possible to use the additives disclosed in JP-A-2013-84349,
JP-A-2009-93983, JP-A-2003-297375 and JP-A-2014-199815.
Herein, the charge-discharge characteristics of the storage battery
and the negative electrode can include not only cycle
characteristics but also characteristics such as input/output
resistance and capacity retention in a charged state. Further, when
the additive enhancing charge-discharge characteristics of the
negative electrode is used, the effect of the present invention is
higher in which a concentration of the additive on the negative
electrode side is high.
The additive can move in the electrolyte through diffusion or
migration, and can move in the electrolyte in a state where a
storage battery is left at rest without charging or discharging.
That is, an additive that is gelated and fixed in the vicinity of
the negative electrode and therefore cannot move to the vicinity of
the positive electrode is not included in the scope of the present
invention. Further, a liquid electrolyte having flowability can be
used since the additive as described above is not fixed to the
vicinity of the negative electrode. Herein, a liquid electrolyte is
one having flowability above a certain level. An electrolyte that
causes the additive to be fixed in the vicinity of the negative
electrode and prevents the additive from moving to the vicinity of
the positive electrode, as described above, is not included in the
scope of the present invention.
The viscosity of the electrolyte in a region of the additive on a
negative electrode side is preferably not too high. By employing a
viscosity at which the electrolyte has the flowability, ion
conductivity can be enhanced and charge-discharge resistance of a
storage battery can be reduced. Further, when the flowability of
the electrolyte is high, the additive on the negative electrode
side easily moves to the positive electrode side, and therefore an
effect of the separator having selective permeability of
suppressing additive movement is remarkable. On the other hand, as
shown in Comparative Example 4 described later, in the electrolyte
which has a viscosity beyond 70 PaS and is gelated by addition of a
gelating agent having a molecular weight of 220000, the additive as
the gelating agent cannot move in the electrolyte through diffusion
or migration, and therefore there is not a remarkable effect by
using the separator having selective permeability.
The additive on the negative electrode side preferably has a
molecular weight which is not too small so that the effect of the
selective permeability of the separator is enough. The molecular
weight is preferably 1000 or more, and more preferably 5000 or
more.
On the other hand, as described above, if an additive having a
large molecular weight is added, the viscosity of the electrolyte
tends to increase to gelate the electrolyte or solubility of the
additive tends to decrease to make it difficult to add an adequate
amount. In such a case, for example, it is possible to disarrange
crystallinity by substituting a monomer of a part of a homopolymer
with another monomer, or increase the solubility of the additive
having a large molecular weight by introducing a functional group
which is higher in a hydrophilic property.
The present invention is applicable to any of a storage battery
having an aqueous electrolyte and a storage battery having a
nonaqueous electrolyte if the storage battery is one having a
negative electrode including, as an active material, at least one
of a metal capable of forming a dendrite and a metal compound
thereof. Hereinafter, an alkaline secondary battery in which the
electrolyte is an alkaline electrolyte solution will be
described.
In the alkaline secondary battery according to the present
invention, the negative electrode preferably contains zinc,
magnesium, aluminum or an alloy thereof. In the case of a zinc
negative electrode, the active material is preferably one or both
of zinc oxide (ZnO) and metal zinc (Zn).
The negative electrode can be prepared, for example, by adding
water, polytetrafluoroethylene and a binder such as a styrene
butadiene rubber to a powder of the above-mentioned negative active
material, a powder of acetylene black, and PbO or the like to
prepare a paste, filling the paste into a substrate of foamed
copper, foamed nickel or the like or applying the paste to a holed
steel sheet, adequately drying the paste, and then subjecting the
resulting material to roll forming and cutting them.
In the alkaline secondary battery according to the present
invention, the positive electrode is preferably nickel, silver
oxide-manganese, air or the like. In the present invention, by
applying the separator having selective permeability to the
additive, it is possible to inhibit the additive in the region on
the negative electrode side from permeating to the region on the
positive electrode side, and therefore a positive electrode whose
maximum operating voltage is 0.4 V or more relative to a potential
of an electrode of Hg/HgO can be used. For example, as the positive
electrode, a nickel electrode composed of a metal hydroxide
containing nickel oxyhydroxide as a main component and a current
collector of foamed nickel or the like; an air electrode composed
of a carbon material, an oxygen reduction catalyst and a binder; or
the like can be used.
An additive amount of the additive in a region on the negative
electrode side varies depending on composition or a molecular
weight of the additive. In accordance with Examples described
later, the amount is preferably 1 g or more as a lower limit, more
preferably 2.5 g or more, and particularly preferably 5 g or more
with respect to 100 ml of the electrolyte. The amount is preferably
15 g or less as an upper limit, more preferably 12.5 g or less, and
particularly preferably 10 g or less.
When the additive amount is 1 g/100 ml of electrolyte or more,
charge-discharge cycle performance can be improved, and when the
additive amount is 15 g/100 ml of electrolyte or less, an excessive
increase of viscosity of the electrolyte can be prevented.
As the electrolyte in the present invention, for example, a
solution obtained by dissolving a hydroxide of an alkali metal in
water can be used, and examples of the hydroxide of an alkali metal
include KOH, NaOH, LiOH and the like, and these compounds may be
used alone or in combination of two or more thereof. The
concentration of the hydroxide is preferably 3M or more as a lower
limit, and more preferably 4M or more. The concentration is
preferably 9M or less as an upper limit, and more preferably 6M or
less. When the concentration of the hydroxide is 3M or more,
self-discharge can be suppressed, and when the concentration is 9M
or less, an increase of viscosity of the electrolyte can be
suppressed.
When the negative electrode contains zinc or an alloy thereof, the
electrolyte preferably contains zinc oxide in a saturated
concentration. When the negative electrode contains zinc oxide,
elution of zinc contained in the negative electrode can be
suppressed.
The separator according to the present invention can be a
semipermeable membrane which is obtained by irradiating a
polyolefin substrate film such as polyethylene, polypropylene or
the like with electron beams accelerated by an electron beam
accelerator in a nitrogen atmosphere to generate radicals, and
immersing the substrate film in a deoxidized acrylic acid solution
to perform graft polymerization. This membrane is an anion-exchange
membrane which the OH ions selectively permeate.
When polyolefin is used as a substrate, a separator having high
oxidation resistance and high alkali resistance can be formed.
Further, in order to adjust a water penetration rate or an air
permeability, a nonwoven fabric or a microporous membrane may be
laminated on the membrane for use.
When the present invention is applied to a storage battery having a
nonaqueous electrolyte, the negative electrode preferably includes
lithium or a lithium alloy as an active material. As the lithium
alloy, an alloy obtained by alloying lithium with Al, Sn, Bi, In,
Ag or the like can be used.
As the active material of the positive electrode, transition metal
compounds such as manganese dioxide and vanadium pentoxide,
transition metal chalcogenide such as iron sulfide and titanium
sulfide, lithium transition metal composite oxides of a
.alpha.-NaFeO.sub.2 type represented by Li.sub.1+XMeO.sub.2
(1.ltoreq.x, Me is one or more transition metals selected from
among Co, Ni and Mn) or a spinel type such as LiMn.sub.2O.sub.4,
compounds obtained by substituting a transition metal site or a
lithium site of these composite oxides with a metal element such as
Al, V, Fe, Cr, Ti, Zn, Sr, Mo, W or Mg or with a non-metal element
such as P or B, and phosphate compounds of an olivine type such as
LiFePO.sub.4 can be used.
A nonaqueous solvent used for the nonaqueous electrolyte can be
selected from solvents commonly used in a nonaqueous electrolyte
battery. Examples of the nonaqueous solvent include, but are not
limited to, cyclic carbonic acid esters such as propylene
carbonate, ethylene carbonate, butylene carbonate, chloroethylene
carbonate, and vinylene carbonate; cyclic esters such as
.gamma.-butyrolactone and .gamma.-valerolactone; chain carbonates
such as dimethyl carbonate, diethyl carbonate, and ethylmethyl
carbonates; chain esters such as methyl formate, methyl acetate,
and methyl butyrate; tetrahydrofuran and derivatives thereof,
ethers such as 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxyethane,
1,4-dibutoxyethane, and methyl diglyme; nitriles such as
acetonitrile and benzonitrile; dioxolan and derivatives thereof,
and ethylene sulfide, sulfolane, sultone and derivatives thereof.
These solvent are usually used as a mixture of two or more thereof
in order to adjust a dielectric constant, viscosity or an operating
temperature region.
Further, examples of an electrolyte salt used for the nonaqueous
electrolyte include inorganic ionic salts containing one of lithium
(Li), sodium (Na), and potassium (K) such as LiClO.sub.4,
LiBF.sub.4, LiAsF.sub.6, LiPF.sub.6, LiB(C.sub.2O.sub.4).sub.2,
LiSCN, LiBr, LiI, Li.sub.2SO.sub.4, Li.sub.2B.sub.10Cl.sub.10,
NaClO.sub.4, NaI, NaSCN, NaBr, KClO.sub.4, and KSCN; and organic
ionic salts such as LiCF.sub.3SO.sub.3,
LiN(CF.sub.3SO.sub.2).sub.2, LiN(C.sub.2F.sub.5SO.sub.2).sub.2,
LiN(CF.sub.3SO.sub.2)(C.sub.4F.sub.9SO.sub.2),
LiC(CF.sub.3SO.sub.2).sub.3, LiC(C.sub.2F.sub.5SO.sub.2).sub.3,
(CH.sub.3).sub.4NBF.sub.4, (CH.sub.3).sub.4NBr,
(C.sub.2H.sub.5).sub.4NClO.sub.4, (C.sub.2H.sub.5).sub.4NI,
(C.sub.3H.sub.7).sub.4NBr, (n-C.sub.4H.sub.9).sub.4NClO.sub.4,
(n-C.sub.4H.sub.9).sub.4NI, (C.sub.2H.sub.5).sub.4N-maleate,
(C.sub.2H.sub.5).sub.4N-benzoate,
(C.sub.2H.sub.5).sub.4N-phthalate, lithium stearylsulfonate,
lithium octylsulfonate, and lithium dodecylbenzenesulfonate, and
these ionic compounds may be used alone or in combination of two or
more of them.
In the present invention, a nonaqueous electrolyte storage battery
is assembled by arranging an electrolyte formed by further adding
an additive to the nonaqueous solvent and the electrolyte salt in a
region on the negative electrode side defined by the separator, a
semipermeable membrane or an ion-exchange membrane, and arranging
an electrolyte in which the additive is not added in a region on
the positive electrode side. In the storage battery, the
concentration of the additive in a region on the negative electrode
side is kept higher than the concentration in a region on the
positive electrode side due to the selective permeability of the
ion-exchange membrane.
EXAMPLES
Example 1
<Preparation of Electrolyte>
A modified polyvinyl alcohol having a molecular weight of 13000
(hereinafter, referred to as "modified PVA-1") as an additive was
charged into pure water, stirred, and thereafter further stirred
raising the temperature to 90.degree. C. After confirming that the
modified PVA-1 was fully dissolved, the modified PVA-1 was cooled
to room temperature to prepare an aqueous solution containing an
additive.
An alkaline solution including a KOH powder dissolved in pure water
was prepared and cooled to room temperature, and then the alkaline
solution was mixed with the above-mentioned aqueous solution
containing the additive and adjusted so that 5.0 g of the additive
was contained in 100 ml of a KOH solution having a concentration of
4M (hereinafter, denoted by "4M KOH").
Moreover, into the resulting solution, a ZnO powder was excessively
charged, and the resulting mixture was stirred at 25.degree. C. for
24 hours. Thereafter, a zinc-saturated electrolyte including the
additive was prepared by removing an excessive ZnO by filtration.
The viscosity of the resulting electrolyte was 4.93 Pas.
The viscosity (absolute viscosity) of the electrolyte is a value
determined by multiplying a relative viscosity by a density. In
addition, in the present experiment, each specific gravity was
measured with use of a hydrometer (DMA500 manufactured by Anton
Paar Japan K.K.). The relative viscosity was measured with use of a
viscometer (AMVn manufactured by Anton Paar Japan K.K.). A
measurement temperature of the specific gravity and the relative
viscosity was 20.degree. C.
<Preparation of Electrode>
Predetermined amounts of a ZnO powder, acetylene black (AB), and a
PbO powder were weighed and stirred. Thereafter, water and a
polytetrafluoroethylene (PTFE) dispersion were added, and the
resulting mixture was further stirred to prepare a paste. The solid
content of the paste was adjusted so that a solid content was
composed of ZnO, AB, PTFE and PbO in proportions of 88:5:5:2 (% by
mass) and a moisture percentage was 65% by mass with respect to the
entire paste. The paste was filled into a foamed copper substrate
having a thickness of 100 mm and a density per unit area of 0.45
g/cm.sup.2, and adequately dried, and then the resulting material
was subjected to roll forming. Thereby, a sheet of ZnO electrode
having a thickness of 0.35 mm was obtained. The substrate was cut
into a size of 2 cm.times.2 cm to obtain a ZnO electrode
(hereinafter, referred to as a "zinc electrode"). The filled amount
of the paste was adjusted so that a theoretical capacity of the
zinc electrode was 100 mAh.
A sinter-type nickel electrode with excessive capacity was used for
the positive electrode.
<Preparation of Ion-Exchange Membrane>
A crosslinked polyethylene film having a thickness of 25 .mu.m was
irradiated with electron beams by 100 kGy (kilogray) at an
accelerated voltage of 300 kV and at a beam current of 10 mA by an
electron beam accelerator in a nitrogen atmosphere, and immersed,
at room temperature for 3 hours, in a solution composed of 20 parts
by weight of acrylic acid, 79 parts by weight of water and 1 part
by weight of a Mohr's salt which had previously been deoxidized by
nitrogen to obtain an ion-exchange membrane formed by graft
polymerization.
<Preparation of Test Cell>
The zinc electrode thus prepared was packed in the form of a bag
using the above-mentioned ion-exchange membrane. Further, a
nonwoven fabric made of fibers of polypropylene and polyethylene
was overlaid thereon in the form of a bag to form a separator. The
above-mentioned electrolyte including the additive added was
injected into the bag of the ion-exchange membrane to such an
extent that the electrode was adequately immersed. A positive
electrode was arranged on both sides of the zinc electrode, and
these electrodes were put in a container, and an alkaline
electrolyte of the 4M KOH not including the additive added was
injected into a region on the positive electrode side of the
container to such an extent that the positive electrode was
adequately immersed. Further, a Hg/HgO electrode was disposed as a
reference electrode. Thereafter, the container was left at rest
until the electrolyte adequately permeated the electrode. Thereby,
an open-type test cell according to Example 1 was prepared.
Example 2
A test cell according to Example 2 was prepared in the same manner
as in Example 1 except that the additive in the electrolyte in a
region on a zinc electrode side was a modified polyvinyl alcohol
having a molecular weight of 10000 (hereinafter, referred to as
"modified PVA-2"). The viscosity of the electrolyte including the
additive added in a region on a zinc electrode side was 2.40
Pas.
Example 3
A test cell according to Example 3 was prepared in the same manner
as in Example 1 except for preparing an electrolyte in a region on
a zinc electrode side by adding 10.0 g of the modified PVA-2 used
in Example 2 to 100 mL of 4M KOH. The viscosity of the electrolyte
in a region on a zinc electrode side was 3.79 Pas.
Comparative Examples 1 and 2
Test cells according to Comparative Examples 1 and 2 were prepared
in the same manner as in Examples 1 and 2, respectively, except for
packing the zinc electrode with a polypropylene microporous
membrane (pore size according to a mercury intrusion method: 0.043
.mu.m) having a thickness of 25 .mu.m in place of the ion-exchange
membrane used in Example 1.
In addition, a permeation test was carried out using the
above-mentioned microporous membrane, and consequently, 11% of
polyvinyl alcohol having a molecular weight of 22000 permeated the
microporous membrane. That is, it was found that the microporous
membrane did not have the selective permeability in the present
invention for the additive having a molecular weight of 22000.
Comparative Example 3
A test cell according to Comparative Example 3 was prepared in the
same manner as in Example 1 except for changing the electrolyte in
a region on a zinc electrode side to an electrolyte in which the
additive was not added. The viscosity of the electrolyte was 1.50
Pas.
Comparative Example 4
Polyacrylic acid (1 g) having a molecular weight of 220000
(hereinafter, referred to as "PAA") was added to 100 ml of the 4M
KOH, and consequently, a gel-like electrolyte having a viscosity
exceeding 70 Pas was obtained. A test cell according to Comparative
Example 4 was prepared in the same manner as in Example 1 except
that the gel-like electrolyte was used.
<Evaluation of Cycle Characteristics>
Cycle tests were carried out in an environment of 25.degree. C.
repeating the following charge-discharge conditions on the test
cells of Examples 1 to 3 and Comparative Examples 1 to 4.
A current was set to 0.5 CmA (50 mA), and the test cell was charged
to 50 mAh at a constant current constant voltage (limited
potential: 1.55 V), rested for 5 minutes, and then discharged so as
to be -0.8 V relative to a reference electrode. A cycle test was
performed under the above-mentioned conditions, and the number of
cycles in which the test cell reached 80% or less of an initial
capacity was defined as a cycle life, and the test cell was
evaluated based on the cycle life.
The results of the cycle test are shown together with the molecular
weight and additive amount of each additive, the separator on the
zinc electrode side, and the viscosity of the electrolyte on the
zinc electrode side in Table 2 described below.
TABLE-US-00002 TABLE 2 Additive Viscosity of Molecular Amount Cycle
Electrolyte Additive Weight g/l00 mL Separator Life Pa s Example 1
Modified PVA-1 13000 5.0 Ion-exchange 140 4.93 membrane Example 2
Modified PVA-2 10000 5.0 Ion-exchange 120 2.40 membrane Example 3
Modified PVA-2 10000 10.0 Ion-exchange 160 3.79 membrane
Comparative Modified PVA-1 13000 5.0 Microporous 90 4.93 Example 1
membrane Comparative Modified PVA-2 10000 5.0 Microporous 90 2.40
Example 2 membrane Comparative None -- 0.0 Ion-exchange 60 1.50
Example 3 membrane Comparative PPA 220000 1.0 Ion-exchange 40
Gelated Example 4 membrane (exceeding 70)
In each of the test cells according to Examples 1 to 3 and
Comparative Examples 1 to 2, the additive for suppressing the
formation of dendrite was added to the electrolyte in a region on
the zinc electrode side. However, in each of the test cells
according to Comparative Examples 1 to 2 including a separator
formed by laminating the microporous membrane on the nonwoven
fabric, it is thought that the additive easily permeated the
separator to a region on the positive electrode side and underwent
oxidative decomposition due to a high potential, and therefore
addition effect did not continue, and the number of cycles reaching
the cycle life was low.
In contrast with this, in each of the test cells according to
Examples 1 to 3 including the ion-exchange membrane for the
separator, it is thought that although OH ions permeate the
ion-exchange membrane, the ion-exchange membrane has the selective
permeability (semipermeability) in which the permeability for the
additive is lower than that for OH ions, and therefore the
permeation of the additive to a region on the positive electrode
side was suppressed to maintain a concentration of an organic
additive on the zinc electrode side, and thereby the cycle life was
long.
In the test cell according to Comparative Example 3, the additive
which provides an effect of suppressing the forming of dendrite was
not added to the electrolyte on the zinc electrode side. Even
though the ion-exchange membrane was used for the separator, the
cycle life was short.
In the test cell according to Comparative Example 4, since the
electrolyte was gelated, the additive did not move in the
electrolyte through diffusion or migration to undergo oxidative
decomposition on the positive electrode, and therefore there was
not a remarkable effect of the separator having selective
permeability.
The storage battery according to the present invention can inhibit
the additive added to the electrolyte in the region on the negative
electrode side from permeating to the positive electrode, since the
storage battery includes a separator made of a semipermeable
membrane or an ion-exchange membrane which permeates ions
contributing to a battery reaction but does not permeate the
additive in the electrolyte solution. Accordingly, it is possible
to suppress the forming of dendrite from the metal contained in the
negative electrode to remarkably improve a cycle life by keeping
the concentration of the additive in a region on the negative
electrode side higher than the concentration in the region on the
positive electrode side. Therefore, the storage battery is expected
to be used as a power supply of electronic equipment, electric
vehicles and the like.
* * * * *